1. Field of the Invention
The present invention relates to a mask- or reticle-free photolithography system that directly writes or forms a pattern on a target object such as a substrate. In particular, it relates to the control of an exposure process.
2. Description of the Related Art
In manufacturing an integrated circuit, a printed circuit board, or photoresist-coated substrate is subjected to photolithography, i.e., an exposure process for imaging a predetermined pattern on the substrate. In a mask- or reticle-free photolithography system, a spatial light modulator with a plurality of two-dimensionally arrayed cells, such as a DMD (Digital Micro-mirror Device) or an LCD (Liquid Crystal Device), is used. Light from a light source is reflected off the modulation cells, each cell (which could be implemented as a mirror, for example) projecting a part of an image on the basis or pattern data.
In the exposure process, a material coated with photoresist is arranged on a table, and the table is moved in a scanning direction relative to the photosensitive material to scan an exposure area that is a projection area of the spatial light modulator. Each cell of the spatial light modulator is modulated, i.e., switched on/off in accordance with the relative position of the exposure area and the pattern data. After the exposure process, a developing process, an etching process, a resist removal process, and so on, are carried out. As for the exposure method, the Step & Repeat process, or the continuous scanning method is used. Furthermore, a multi-exposure method that repeatedly illuminates light on the same area may be utilized.
In a photolithography system connected with a CAD system, pattern data (e.g., vector data) is transmitted to the photolithography system, and the pattern data is converted to the raster data used for controlling the light modulation calls each of the light modulation cells (which may be a micro-mirror) is controlled by the corresponding raster data. Input of the pattern data, processing of the pattern data, and the control of the cells are repeatedly performed in accordance with the relative movement of the exposure area. Namely, the pattern data is renewed every time the exposure area reaches a predetermined area to be exposed. These photolithography systems are disclosed in Japanese Patent publications, No. 2003-57836A, No. 2003-15309A.
The frequent renewal of enormous quantities of pattern data takes a lot of time, and influences the total exposure time, i.e., throughput. To reduce the load of the data process, for example, vector data having coordinate information is subjected to a coordinate transform process, and a part of the transferred vector data is sampled. Also, the reflection surface of a DMD is divided into a plurality of areas, and mirrors are reset in each area after raster data is transmitted to the mirror. These photolithography systems are disclosed in Japanese Patent publication No. 2005-84198A and No. 2005-55881.
The spatial light modulator is composed of many cells (for example, 1024×768 cells). The amount of raster data and the memory capacity required for storing the raster data depend upon the number of cells. Furthermore, a plurality of spatial light modulators is arranged in a photolithography system since the exposure area is small compared to the substrate, and pattern data and memory should be prepared in accordance with the number of spatial light modulators. Therefore, the data-transform process for generating raster data and the data-transmission process need an enormous amount of time, and throughput is not improved. Particularly in the case of the multi-exposure method, the frequency of the data-transmission and data-transform processes is large compared with the shot-exposure method. Consequently, the relative movement of the table and exposure pitch is restricted due to the long period required for processing of the data.